public class ListNode {
    int val;
    ListNode next;

    ListNode() {
    }

    ListNode(int val) {
        this.val = val;
    }

    ListNode(int val, ListNode next) {
        this.val = val;
        this.next = next;
    }


    public class MergeTwoLinkedLists {
        public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
            ListNode newHead = new ListNode(-1);
            ListNode tmp = newHead;
            while (list1 != null && list2 != null) {
                if (list1.val < list2.val) {
                    tmp.next = list1;
                    list1 = list1.next;
                    tmp = tmp.next;
                } else {
                    tmp.next = list2;
                    list2 = list2.next;
                    tmp = tmp.next;
                }
            }
            if (list1 != null) {
                tmp.next = list1;
            }
            if (list2 != null) {
                tmp.next = list2;
            }
            return newHead.next;
        }
    }
}
